The present invention relates to an image photographing apparatus, and more particularly to an image photographing apparatus including a transformer as a power supply for energizing the image photographing apparatus, the transformer being spaced from an image monitor as much as possible and oriented such that the direction of leakage fluxes from the transformer will be substantially parallel to the direction of an electron beam radiated in a display tube for allowing an image to be displayed accurately on the monitor.
There have widely been used in recent years image processing systems in which image information created by computerized tomography (CT) is displayed on a CRT monitor and photographed on a photographic photosensitive medium by an image photographing apparatus. The image processing system includes the image photographing apparatus, an image input unit such as a medical diagnostic unit, an image information processing unit for processing image information from the image input unit to produce an image to be displayed on the CRT monitor, and an automatic image developing unit for developing photographed images on the photosensitive medium.
In the image photographing apparatus, the photosensitive medium such as a photographic film supplied from a supply magazine is exposed to a plurality of images displayed on the CRT monitor. More specifically, a photographic film supplied from the supply magazine is fed by a film feed mechanism into an image forming region in which the film is positioned in place by a film presser plate which is displaceable vertically toward and away from the film.
The CRT monitor which serves as a light source for producing image information and a focusing or image forming lens jointly serve as an image-forming optical mechanism in the image forming region. A plurality of pieces of image information which are successively displayed on the CRT monitor are successively photographed on the film in respective areas thereon by the image-forming optical mechanism.
The film on which the pieces of information are photographed is then released by moving the film presser plate downwardly, and delivered by the film feed mechanism into a receiving magazine positioned substantially horizontally below the supply magazine. Then, the film is transferred into the automatic image developing unit. Alternatively, the film may be transferred from the image forming region directly into the automatic image developing unit.
The CRT monitor in the image photographing apparatus is generally energized by a direct current under a relatively low voltage. To obtain such a direct current from a commercial AC power supply having a voltage of 100 V, for example, the voltage of 100 V has to be dropped to a certain voltage, and then the alternating current has to be rectified. Consequently, the image photographing apparatus requires a transformer for reducing the voltage of the commercial power supply.
Since the transformer increases or reduces the applied voltage through electromagnetic induction, magnetic fluxes leaked from the transformer are present around the transformer. The flux leakage tends to cause the electron beam which is cyclically deflected in the CRT monitor to be displaced out of position, thus disturbing the image displayed on the CRT screen.
When an image displayed on the CRT screen is photographed or recorded on the film for use in medical diagnosis, the raster on the CRT screen will present an obstacle to the process of diagnosis based on a visual inspection of the displayed image. Such a problem is solved by interpolating the raster to make it less noticeable. However, if the electron beam is undesirably displaced under the influence of the flux leakage from the nearby transformer, then it becomes impossible to effect the interpolation for rendering the raster less conspicuous. One solution is to surround the CRT monitor or the transformer with a magnetic shield made of a ferromagnetic material to permit a desired image to be displayed with accuracy on the CRT screen. This proposal is however disadvantageous in that since the ferromagnetic material is comparatively expensive, the cost of manufacture of the image photographing apparatus is likewise comparatively expensive, and is increased in weight.